java中的字符串索引越界错误（charAt）

Question

Quick question. I have this code in a program:

input = JOptionPane.showInputDialog("Enter any word below")
int i = 0;  
for (int j = 0; j <= input.length(); j++)  
{
    System.out.print(input.charAt(i));  
    System.out.print(" "); //don't ask about this.  
    i++;
}   

• Input being user input
• i being integer with value of 0, as seen

Running the code produces this error:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 6
at java.lang.String.charAt(Unknown Source)
at program.main(program.java:15)

If I change the charAt int to 0 instead of i , it does not produce the error...
what can be done? What is the problem?

Answer 1

Replace:

j <= input.length()

... with ...

j < input.length()

Java String character indexing is 0-based, so your loop termination condition should be at input 's length - 1.

Currently, when your loop reaches the penultimate iteration before termination, it references input character at an index equal to input 's length, which throws the StringIndexOutOfBoundsException (a RuntimeException ).

Answer 2

String indexing in Java (like any other array-like structure) is zero-based . This means that input.charAt(0) is the leftmost character. The last character is then at input.charAt(input.length() - 1) .

So you are referencing one too many elements in your for loop. Replace <= with < to fix. The alternative ( <= input.length() - 1 ) could bite you hard if you ever port your code to C++ (which has unsigned types).

By the way, the Java runtime emits extremely helpful exceptions and error messages. Do learn to read and understand them.

Answer 3

Replace for loop condition j <= input.length() with j < input.length() , as string in Java follows zero based indexing. eg indexing for the String "india" would start from 0 to 4.

Answer 4

You were accessing the array from [0-length], you should do it from [0-(length-1)]

int i = 0;
for (int j = 0; j < input.length(); j++)
{
    System.out.print(input.charAt(i));
    System.out.print(" "); //don't ask about this.
    i++;
}

Answer 5

Try the following:

j< input.length() 

and then:

int i = 0;
for (int j = 0; j < input.length(); j++)
{
    System.out.print(input.charAt(i));
    System.out.print(" "); //don't ask about this.
    i++;
} 

Answer 6

Use this;

for (int j = 0; j < input.length(); j++)
{
    System.out.print(input.charAt(j));
    System.out.print(" "); //don't ask about this.
}

Answer 7

for (int j = 0; j < input.length(); j++)
{
    System.out.print(input.charAt(j));
    System.out.print(" "); //don't ask about this.
}